This invention relates to a system for acquiring data from a plurality of sources simultaneously.
The invention was developed for use in a physiological data acquisition system but it has many other applications as well.
A typical use of the invention is in connection with cardiac monitoring of a plurality of bedridden patients in a cardiac care unit. In such cases it is customary to transmit electrocardiograph (ECG) data to a central station processor for determining if the heart is exhibiting arrhythmia or other abnormalities. One use of the signals is to display the analog ECG on a cathode ray oscilloscope along with ECG waveforms of other patients.
It is known in the prior art to use the analog ECG signals derived from the patient to frequency modulate (FM) a carrier wave for transmitting the ECG values to the central monitoring station. At the monitoring station, it is necessary, on some occasions, to demodulate the FM signals and convert to digital or analog equivalents of the original analog ECG or whatever physiological parameter is being monitored. In some installations, dozens of patients must be monitored at a central station simultaneously. The conventional approach was to demodulate the respective FM signals and then perform an analog-to-digital conversion. The disadvantage of this approach is that dozens of demodulators may be required in order to supply enough data to meet the required digital data rate. Moreover, a plurality of multiplexers are required to switch the demodulated FM to the analog-to-digital (A/D) converter. This approach requires a large amount of circuit board area which is obviously disadvantageous. Moreover, adjustment of the demodulators is difficult and repeatability from unit to unit is often unreliable.
A further disadvantage of the foregoing and other prior art approaches is that one or more rather costly A/D converters must be used or time-shared.